Exploring the Possibilities of 14C Bomb-Pulse Dating of Human Tissue Samples

Abstract: The testing of nuclear weapons in the atmosphere, in the middle of the 20'h century, resulted in a bomb-pulse excess of atmospheric 14C. A bomb-pulse dating method was thus developed. The latter is a method to determine the time of formation of formerly living modern (i.e. living after 1955) material , based on the 14C/ 12C ratio in it. The objective of this work was to evaluate the factors that can affect the accuracy of bomb-pulse dating of samples originating from the human body. This method may be useful in medicine, for example, to elucidate the progress of an illness. Special importance was given to the effect of diet since the ingestion of food is the main pathway in which carbon enters the human body. Investigation of the diet may reveal the consumption of particular foodstuffs, such as marine ingredients, for example, that may have a different 14C/ 12C ratio from the local atmospheric one. A literature investigation was carried out of the 14C/ 12C ratio in the atmosphere and oceans at different geographical locations showing that ordinary intake of marine foodstuffs can lead to age alteration (atmospheric predicted age - diet predicted age) from -2.4 to 1.4 years. 14C/ 12C measurements were also conducted on blood serum from Swedish subjects and atherosclerotic plaque samples from Swedish and Portuguese patients. It was concluded from the blood serum study that the diet of the subjects studied can influence bomb-pulse dating results due to the marine effect, which leads to a time lag (positive or negative) due to the different 14C/ 12C ratio of marine food compared to terrestrial food. This effect can lead to samples after 1963 (the year of the Limited Test Ban Treaty) appearing to be younger, while samples before 1963 appear to be older. The average age deviation (CAL!Bomb date- sampling date) of the blood serum samples was found to be -1.5 ± 0.7 years. The kind of tissue analysed also plays an important role, since carbon turnover times vary in different tissues and organs. Study of atherosclerotic plaque samples from different plaque regions was performed. On average, cap fragments were the youngest (average age 5.54 ± 2.6 years), core fragments were older (average age 7.79 ± 3.7 years) and interface to media fragments were the oldest (average age 9.74 ± 2.4 years). A comparison between atherosclerotic plaque samples and blood serum samples was also performed, confirming the potential influence of the sort of tissue in bomb-pulse dating. Finally, differences were observed in 14C/12C ratios in the same type of samples (plaque) from subjects with different dietary habits (Portuguese and Swedish diets), reinforcing the concept of dietary influence on bom b-pulse dating. A correction of the bomb-pulse dating, with the aid of o13C values for the blood serum samples of this work, was also attempted. The results appeared to be eligible but confirmed that many factors, except for the diet, are potentially affecting the carbon content of samples from the human body.